Pepsilover - appened to me a couple of times. Just one of those things you have to deal with when using a tablet.
kiki - copy the books from your card to your computer and then hook up your Arc to the computer and copy the books somewhere (the Downloads directory would probably be best so that the Kobo or other reading app can find it easily) like you would with any other media. Or just go to that site while on your Arc and download them again, of course.